London Bus change over to DMR

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Re: London Bus change over to DMR

Postby Alfie » Tue Nov 27, 2018 11:51 pm

ps. anyone who has listened to london buses know the problems they have with weak transmissions and interference. why add voice degradation for privacy when this system does not need and has never needed privacy ? there are also a few cases where unauthorised users ie not bus drivers have heard info and acted on it stopping/solving crime and other incidents. dont know of any listeners causing harm just good or casual/old timers who enjoy the listen. its public transport not mi5 or kgb.
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Re: London Bus change over to DMR

Postby Metradio » Wed Nov 28, 2018 5:42 pm

Out of interest the installed DMR equipment is made and supplied by Tait ....

https://www.taitradio.com/

Mike
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Re: London Bus change over to DMR

Postby bigboyblue » Thu Nov 29, 2018 12:21 am

Alfie wrote:voice degradation is a fact with enhanced encryption which is admitted and acknowledged by users, experts and Motorola themselves

Basic is not so noticeable but still has its issues which you can look into

everyone who has used mototrbo/dmr knows what i mean when i say dalek as in the common bad decode it has and this happens more even at a basic enc level at the same range with encode delay and much further at advanced level with added delay. without enc dmr will turn robotic and unintelligible where analogue would still be weak but readable. adding basic enc adds this and a delay and with enhanced enc this is a lot more.

i am not a radio engineer but i can tell you we have had an intense check on our systems. we have an internet linked dmr system and on some far out units enc has been disabled. they can talk and hear on our normal enc channels as they have the enc code programed but they transmit in clear as using enc is less unintelligible. this has been real tested by the radio engineers so i know it to be true as it has been advised and adopted by my workplace on those grounds.


This is a bit off topic as Tait won the radio contract for units, but from the Motorola system planner:

Basic Privacy uses only one key, which is known to both the sender and the receiver. This eliminates
the need to transport cryptographic parameters (for example, Key Identifier) with the voice or data
payload. A voice message, in case of Basic Privacy, neither requires any modification in the payload
nor any additional headers. Therefore, the System Access Time and the audio quality of a Basic
privacy protected voice is same as that of an unprotected voice.


Depends on what they consider as their encryption, as to if it affects the payload.
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Re: London Bus change over to DMR

Postby Davie Boy » Thu Nov 29, 2018 5:04 pm

bigboyblue wrote:in case of Basic Privacy, neither requires any modification in the payload
nor any additional headers. Therefore, the System Access Time and the audio quality of a Basic
privacy protected voice is same as that of an unprotected voice.


Are you really sure about that...? Using Basic Encryption on DMR does not affect essential communications in any way(s) at all...?

How about with basic analogue and CTCSS and DCS codes... would you also say they do not affect essential communications in any way...?
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Re: London Bus change over to DMR

Postby Metradio » Fri Nov 30, 2018 7:37 pm

Looks like they are in the midst of changing over today, many channels now DMR..

Mike
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Re: London Bus change over to DMR

Postby bigboyblue » Fri Nov 30, 2018 7:38 pm

Davie Boy wrote:
bigboyblue wrote:in case of Basic Privacy, neither requires any modification in the payload
nor any additional headers. Therefore, the System Access Time and the audio quality of a Basic
privacy protected voice is same as that of an unprotected voice.


Are you really sure about that...? Using Basic Encryption on DMR does not affect essential communications in any way(s) at all...?

How about with basic analogue and CTCSS and DCS codes... would you also say they do not affect essential communications in any way...?


That's a direct copy and paste from the Motorola system planner document itself. Theres a more detailed explanation as well and also goes into how the enhanced encryption works, and also AES256 encryption does too.


CTCSS and DCS - well as you cant hear those frequencies, then I would say no as well.
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Re: London Bus change over to DMR

Postby brian-w » Sat Dec 01, 2018 11:40 am

Metradio wrote:Looks like they are in the midst of changing over today, many channels now DMR..

Mike

I've heard a couple of controllers complaining that this new digital system is worse than the old one. From the odd snippiets I've heard, it tends to be poor audio from mobiles. Not sure if they're vox operated, but sometimes the first word of a tx gets lost. One mobile was asked her duty number and it took 4-5 goes to convey 1-1-2, with the initial '1' being clipped by the system.
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Re: London Bus change over to DMR

Postby Metradio » Sat Dec 01, 2018 1:30 pm

I don't think they use VOX units, the problem is probably users getting used to the set up TX time - push PTT, wait for Call Permit tone, speak... and not waiting for the tone..

Mike
Connect Systems CS750 and CS800, Hytera PD-365, Motorola DP4600.
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Re: London Bus change over to DMR

Postby Davie Boy » Sun Dec 02, 2018 8:06 pm

bigboyblue wrote:That's a direct copy and paste from the Motorola system planner document itself. Theres a more detailed explanation as well and also goes into how the enhanced encryption works, and also AES256 encryption does too.


Thanks for that... Motorola have been elaborate with claims in the past... Radio engineers tend to differ on that opinion... the one that I know does in any case... and I have experience of a similar scenario Alfie mentioned where basic privacy on a Moto Cap+ system has been dropped and communications and decoding has got better... I will look into this more...

bigboyblue wrote:CTCSS and DCS - well as you cant hear those frequencies, then I would say no as well.


Actually CTCSS and DCS do affect essential communications... which is why the fire service never used them on analogue fireground... there is a delay before the squelch opens... even more so with DCS... this is why we took DCS off our analogue radios as the delay before opening the squelch was very noticeable...
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Re: London Bus change over to DMR

Postby bigboyblue » Mon Dec 03, 2018 6:24 pm

Davie Boy wrote:
bigboyblue wrote:That's a direct copy and paste from the Motorola system planner document itself. Theres a more detailed explanation as well and also goes into how the enhanced encryption works, and also AES256 encryption does too.


Thanks for that... Motorola have been elaborate with claims in the past... Radio engineers tend to differ on that opinion... the one that I know does in any case... and I have experience of a similar scenario Alfie mentioned where basic privacy on a Moto Cap+ system has been dropped and communications and decoding has got better... I will look into this more...

bigboyblue wrote:CTCSS and DCS - well as you cant hear those frequencies, then I would say no as well.


Actually CTCSS and DCS do affect essential communications... which is why the fire service never used them on analogue fireground... there is a delay before the squelch opens... even more so with DCS... this is why we took DCS off our analogue radios as the delay before opening the squelch was very noticeable...


There was a time with the very early firmware, where as you've said, voice (although Motorola always says it doesn't) was worse to listen to with privacy on - although Motorola denied it, there were lots of reports of it.

Make sure all your subscribers and repeaters are up to the latest firmware, and having just tried it with some different handsets, I can confirm its no different, so whatever it 'was' has now been fixed.
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